Small or laboratory scale automated fluid formulating devices are known in combinatorial chemistry operations, the pharmaceutical industry, and in high throughput screening systems used in agricultural and other such similar research areas. The common thread through all of these areas of technology is that the fluids they deal with have very low solids and very low viscosities. These fluids, as typified by water, have viscosities that are independent of the shear rate and generally have viscosities of 1 centipoise. These are referred to as Newtonian fluids because their viscosities are shear independent.
When attempting to formulate high viscosity, high solids fluids, such as slurries and colloids, certain inherent design and processing elements preclude the use of equipment which is commonly used for processing Newtonian fluids. When the fluid is Newtonian, the dispensing and mixing system can consistently and accurately measure whatever amounts might be called for. Problems result from the fact that non-Newtonian fluids, such as slurries and gels, are very shear sensitive. When high viscosity, high solids fluids are subjected to the shear forces caused by forcing these types of fluids through tubing under pressure, the viscosities of such fluids will change. This alteration in viscosity is unpredictable and will impact the measurement of the fluids moving through the tubing. Shear variations can distort volumetric measurements of these fluids. Since devices that measure out quantities of fluid ingredients based on volume are very sensitive to changes in viscosity, the accuracy of each measured aliquot cannot be assured, whether it's for a single dose in a specific formulation or for repeated doses in multiple formulations. The final formulation sample might therefore not correspond exactly to the desired formulation.
It is also important for the proper functioning of volume sensing systems that they remain free of fouling or clogging of their internal components. The cleaning of mixing devices designed for use with low viscosity, low solids fluids may be accomplished with ease. Cleaning is simply achieved by flushing internal components with water or a suitable solvent. Another problem that must be addressed when processing high viscosity, high solids fluids in the system described above relates to the issue of cleaning. High viscosity, high solids fluids will form films on the internal surfaces of the components of fluid dispensing and mixing systems designed to process low viscosity fluids. These films are very difficult to remove by simple flushing. Disassembly of the clogged components is often the only way to remove these deposits. Even this process, however, is only of value for a relatively short time because deposition will occur over and over. If not kept clean, these material deposits on internal tubing or at the dispensing nozzles will severely restrict or completely stop the flow of fluids. Since these types of systems are volume sensitive, the film buildup will displace free flowing fluid. The inaccurate measurement of ingredients will then result, producing a formulation product which will not correspond to the desired formulation. The operator may not, if ever, become aware of this problem until numerous quantities have already been dispensed.
An attempt to resolve some of the aforementioned problems is manifested in a machine used for processing high viscosity colorants for paints. It is commonly referred to as a tinting machine and may be found in the paint department of a hardware store. This type of machine uses high pressure pumps to move high viscosity fluids. While changes in the viscosities of the various tints may be acceptable in a paint tinting operation, such viscosity variances, which then might cause inaccurate volumetric measurements, cannot be tolerated in a precision fluid formulation generating system.
Further, the number of ingredients which can be used as formulation precursors in devices such as tinting machines is limited by the maximum number of dispensing vessels that can be installed onto the device. If a change in one of the ingredients is required, the entire dedicated pump, fluid reservoir and tubing system would have to be removed and cleaned, which is very time and labor intensive. The ability to work with a large variety of fluid precursor ingredients is therefore severely restricted.
What is therefore needed is an automated fluid formulating system which can accommodate the processing of a great number and diversity of fluid precursor ingredients required to prepare high viscosity, high solids fluid formulations. The fluid formulating system must be able to accurately measure quantities of shear sensitive, high viscosity fluids, must be easy to clean when changing from one formulation to another without having to disassemble any part or section of the device.